The speed of the vibration type actuator changes according to the amplitude of the vibration wave, which is excited by the vibrating member. Therefore, the vibration type actuator is controlled by changing the amplitude or frequency of the AC voltage applied to the electrical-mechanical energy conversion element provided in the vibrating member.
In the control of this vibration type actuator, there are often used a method of controlling the vibration type actuator by changing the frequency of the AC voltage in order to reduce the effect of the resonant frequency variation of the vibrating member caused by a temperature or an individual difference in the resonant frequency of the vibrating member.
If a resonant frequency of the vibrating member or an internal loss thereof changes due to a change in the temperature in this control method, a change occurs in a frequency difference between the frequency of the AC voltage and the resonant frequency of the vibrating member even after controlling the frequency of the AC voltage applied to the electrical-mechanical energy conversion element in order to make the speed constant. This causes a change in the circuit efficiency or a variation in frequency-response characteristic.
Given this situation, PTL 1 suggests a controlling device for a vibration type actuator as described below.
This controlling device detects the vibration state of a vibrating member by using a vibration detector sensor and controls the frequency of an applied voltage so as to follow a change in the resonant frequency of the vibrating member while controlling a pulse width corresponding to the amplitude of the applied voltage so that the speed of the vibration type actuator is a desired speed.
Moreover, PTL 2 suggests a device which sequentially identifies a change in the DC gain out of the frequency-response characteristics of the rotational speed relative to the amplitude of the applied voltage of the vibration type actuator on the basis of the ratio of the speed to the amplitude of the applied voltage and then controls the frequency of the applied voltage to stabilize the change in the DC gain.
This enables a reduction in variation in open-loop transfer gain of a speed control loop so that the device is able to follow an environmental change caused by a change in the temperature or an individual difference.